1992 Eldorado alarm won't shut off

I recently purchased a 1992 Eldorado which the previous owner had parked for 2 years because the alarm would go off after starting the car. He unplugged the horns, and just drove it with the lights flashing. After about 3 minutes, the lights would quit flashing. I have pulled every fuse related to security under the hood, including the ones under the large plastic cover. I did the same with the ones in the trunk. Whenever I found one that disarmed it, and pulled it, the starter would not engage. It seems to arm after using the power door locks. I would like to disarm it, or, if not feasible, possibly fix it. I cannot afford to go to the dealer. I do not have a key fob, and only have the chipped key and a trunk key. Thank you in advance.

this is copied from the 1993 Eldo Owners Manual - the 1992 should be identical -the theft deterrent system won’t arm if you lock the doors with a key or manual door lock.
It arms only if you use a power door lock switch or Keyless Entry System.

If you don’t want to arm the theft deterrent system,
the vehicle should be locked with the door key after the doors are closed.